1. Field of the Invention
The present invention relates to a stator of a rotating electrical machine where a cylindrical shape stator winding is enclosed inside a cylindrical shape stator core having no slots, and in particular to effective technology for improving heat dissipation of the stator, and effective technology for protecting an end portion of the stator winding from damage due to stress concentration.
2. Description of the Related Art
Heretofore, as effective technology for improving heat dissipation of a stator, there is known a stator of an electrical rotating machine as disclosed in Japanese Patent Application, First Publication No. Sho 53-54705.
This stator has a construction in which a heat conducting member is inserted between a casing (yolk) and a stator winding (coil). By closely contacting not only between the stator core and the stator winding, but also over the whole region between the casing and the stator winding, the heat dissipation is significantly improved.
This stator however is one having so called slots, and while the heat conducting material is inserted between the casing and the stator winding, the heat conducting material is not inserted between the stator winding and the stator core. Hence this gives a construction where the temperature distribution varies along the circumferential direction of the stator.
Consequently if at the time of operation, distortion due to heating occurs, there is the likelihood of the casing and the stator winding which are closely contacted via the heat conducting member separating, resulting in a drop in heat dissipation.
On the other hand, with a conventional slotless stator, in the case where a cylindrical stator winding is accommodated inside a cylindrical stator core having no slots, in order to secure the insulation between the stator core and the stator winding, an insulation paper (for example a Nomex sheet made by Dupont) is inserted between the stator core and the stator winding.
However, while this insulation sheet has sufficient insulation, thermal conductivity and flexibility are lacking so that it is not possible to maintain a close contact between the stator core and the stator winding. Therefore an air space occurs at the interface, which obstructs heat dissipation.
Moreover, the slotless stator is generally formed by inserting the stator winding into the stator core having no slots, and then inserting a mandrel into the stator winding. Then with these in a held together condition, impregnating and hardening a resin.
However, when the mandrel thermally expands at the time of heat hardening, the end portion of the stator winding is pressed against the stator core edge portion (the intersection ridge line portion between the inner peripheral face and the end face), so that stress is concentrated at the portion pressing against the edge portion. Therefore, there is the case where the stator winding is damaged and the insulation layer lost, resulting in shorting.
The present invention takes into consideration the above situation, with the object of improving heat dissipation of the stator, and protecting the end portion of the stator winding from damage due to stress concentration.
In order to achieve the above objects, the present invention adopts the following means.
That is, according to the present invention, a stator of a rotating electrical machine is provided which comprises a cylindrical stator core having no slots, a cylindrical stator winding accommodated inside the cylindrical stator core, and a heat dissipating sheet inserted between the stator core and the stator winding.
With this construction, since the heat dissipating sheet is inserted between the stator core having no slots and the stator winding, variations in temperature distribution along the circumferential direction of the stator at the time of operation can be suppressed. Hence the close contact condition between the stator core and the stator winding can be more reliably maintained, and the heat generated in the stator winding can be effectively transmitted via the heat dissipating sheet, thus improving heat dissipation.
With this construction, in the case where the heat dissipating sheet contains a filler having good thermal conductivity, heat dissipation can be improved without causing a drop in strength or insulation properties. Moreover, with the above construction, in the case where the heat dissipating sheet is made from a rubber type material having flexible properties, being deformable by pressing, one surface thereof can be closely contacted with the stator winding so as to replicate the irregularities thereof, while the other surface can be closely contacted with the stator core. Therefore the heat dissipation can be further improved while maintaining insulation properties.
The heat dissipating sheet having the above properties is one which can be obtained by mixing a matrix resin with a heat conducting filler. More specifically, for the matrix resin a natural rubber or a synthetic rubber such as butadiene rubber, nitrol rubber, butyl rubber, silicone rubber, fluororubber, or acrylic rubber may be used.
Moreover, for the heat conducting filler, boron nitride, aluminum nitride, or alumina may be used.
In particular, in the case where silicone rubber sheet is used for the heat dissipating sheet, due to the elastic deformation thereof, one surface is closely contacted with the stator winding so as to replicate the irregularities thereof, and the other surface is closely contacted with the stator core. Therefore, the heat dissipation is even more improved. Furthermore, a silicone rubber sheet is also suitable from the point of having excellent thermal tolerance even if this becomes exposed to a high temperature with the stator winding generating heat, and from the point of not generating noxious gasses due to not containing halogens or the like.
Moreover, for the heat conducting filler, boron nitride having high thermal conductivity, and excellent electrical insulation properties, chemical stability, and filler properties, which is widely used for electrical insulation purposes, and as a heat dissipating filler, is ideal.
A silicone heat dissipating sheet having such a construction is marketed for use in transistor heat dissipation and the like. For example, it is possible to use a heat dissipation silicone rubber sheet made by the Shin-Etsu Chemical Co. Ltd. (TC-BG type) or a heat dissipating sheet made by Denka (BFG type).
Furthermore, with any of the above constructions, in the case where a protective sheet is further inserted between the end portion of the stator core and the end portion of the stator winding, the end portion of the stator winding is reinforced by the protective sheet. Therefore, even if a stress concentration occurs in part of the stator, the stator winding can be effectively prevented from being damaged.